I don't see how to shorten Phil's post all that much and still preserve the essence, so here's a largely intact excerpt:
Last year I wrote about the nifty website Ficly, a community where you can write short fiction. And I mean short: each story can only be 1024 characters — roughly 200 words or so. It’s incredibly limiting, which means you really have to be careful when you write.
The story I wrote then was loosely based on the last chapter of my book Death from the Skies!. I’ve been playing around again, and have recently become interested in zombies. Since I’m a scientist, of course I had to put my own spin on it… and I was curious if it was possible to have an overarching theme to a story when it was so short. I think the answer is: barely. So here, in its entirety, is my new Ficly, "Random Walk".
I know a mathematician’s an unlikely survivor. But it’s not axiomatic.
By the time I realized I was in trouble, there was only one way to go: up. I locked the door, made sure the windows were secure, and ran up to the second floor.
I peeked out a bedroom window at the rotting, writhing mass below. I should’ve predicted this, I guess, but in my defense I didn’t know all the initial conditions.
I didn’t see how the pile got started. Extrapolating backwards, I can guess it was one of the deadwalkers in advanced decay. It bumped into the house and fell apart. There must’ve been hundreds before who stayed intact, but statistics won’t be denied.
Once seeded, it grew. Another fell, and another. They don’t climb, really, but they can walk up hill. One on the pile, then another. Given their speed, average size, direction, I can calculate how long before they’ll reach this window in front of me: 6 to 8 days. Plus or minus.
I have 7 days of food here. I suspect in week or so, I’ll have one last equation to solve.